This invention is in the field of magnetorheological materials, in particular magnetorheological materials comprising a supramolecular polymer gel and/or magnetizable particles coated with a supramolecular layer.
Magnetorheological materials are typically comprised of magnetizable particles suspended in a carrier material. A magnetorheological material exhibits rapid and reversible changes that are controllable by an applied magnetic field. The shear stress and viscosity of such a material is related to whether the material is in the presence of a magnetic field, termed the on-state, or the absence of a magnetic field, termed the off-state. In the on-state, the magnetizable particles align with the magnetic field and increase the shear yield stress and viscosity of the material over its off-state value.
Typical state-of-the-art magnetorheological (MR) fluids are multiphase materials consisting of magnetizable particles suspended in a liquid carrier fluid. These MR fluids exhibit properties typical of a viscoelastic material. In addition to the magnetizable particles, the carrier fluid serves as a continuous insulating material. Some of the carrier fluids typically utilized are silicone, hydrocarbon, and synthetic oils. An additional component that is often present in MR fluids is a stabilizer, which serves to keep the particles suspended in the fluid. MR fluids demonstrate non-Newtonian fluid behavior when exposed to a magnetic field.
Magnetorheological materials containing chemically cross-linked gels have been reported. U.S. Pat. No. 6,527,972, to Fuchs et al. discloses magnetorheological polymeric gels (MRPGs) comprising magnetic particles and a carrier material comprising a partially covalently-crosslinked polymeric gel.
Magnetorheological materials containing materials with some non-covalent bonding or cross-linking have also been reported. U.S. Pat. No. 5,645,752, to Weiss et al. reports hydrogen-bonding thixotropic agents including silicone oligomers, organic oligomers, and organo-silicon oligomers. WO 97/02580 to Zrinyi et al. reports magnetic field sensitive gels wherein the gels comprise a polymer cross-linked by physical and/or chemical means. JP410296074A to Zuriini et al. reports polymer substances with a cross-linking structure and a magnetic colloidal particle dispersed in the cross-linking structure, where the polymer substances include agar and gelatin.
Ginder et al. (U.S. Pat. No. 5,549,837) and Foister (U.S. Pat. No. 5,667,715) report MR fluids with magnetic particles of more than one size range in a carrier fluid. Ginder et al. disclose a MR fluid composition comprising a magnetizable carrier fluid and a multiplicity of magnetizable particles loaded within the magnetizable carrier fluid. The magnetizable carrier fluid can be a ferrofluid. Foister discloses a MR fluid employing a mixture of a first component of relatively large particles and a second component of relatively small particles, dispersed in a liquid vehicle.
Coating of iron and/or iron oxide particles with monolayers of long chain thiols or imidazolines is reported by Kataby et al. (G. Kataby et al., Langmuir, (1997), 13, 6161-6158; G. Kataby et al., (1998), Thin Solid Films, 333, 41-49). Self-assembled coatings of iron nanoparticles by carboxylic acids and long-chain alcohols have also been reported (G. Kataby et al., “Coating carboxylic acids on amorphous iron nanoparticles,” (1999) Langmuir, 15, 1703-1708; G. Kataby et al., (1997)—Langmuir 14, 1512 (1998).
Use of surfactant bilayers for stabilization of magnetic fluids was reported by Shen et al. (Shen, L. et al., (1999), Langmuir, 15, 447-453). Polymerization of olefin-terminated surfactant bilayers on magnetic fluid nanoparticles has also been reported (Shen, L. et al., 2000, Langmuir, 16, 9907-0011). U.S. Pat. No. 6,527,927, to Fuchs et al. discloses magnetorheological materials comprising magnetic particles coated with surfactant bilayers and a carrier material comprising a polymeric gel.
U.S. Pat. No. 5,106,691 to Harwell et al. reports a method for producing polymeric films from a surfactant template. Experiments were reported for sodium dodecyl sulfate as surfactant, styrene (with ethanol) as monomer and alumina powder as substrate. Polymerization of monomers adsolubilized within bilayers formed on particles is reported by Megure et al. and Wu et al. (Megure, et al (1986), Bull. Chem. Soc. Jpn. 59, 3019; Wu et al., (1987), Langmuir, 3, 531, Wu et al., (1987), J. Phys. Chem. 91, 623).
U.S. Pat. No. 6,527,927, to Fuchs et al. discloses magnetorheological materials comprising magnetic particles coated with monolayers, self-assembling monolayers, bilayers or multiple layers of a polymeric gel. U.S. Pat. No. 5,985,168 describes the use of a bridging polymer to modify the surface of the iron particles. This approach is reported to lead to improved stability and redispersibility. In this patent three thermoset polymers are described: polyvinylpyrollidone, polyethyleneamine and poly(4-vinlypyridine). Organic polymers have also been reported as coatings for iron particles, as described in U.S. Pat. No. 5,989,447. This patent describes many families of polymers which are used and exhibit reduced abrasiveness and produce high stability with regard to settling. The use of polyelectrolytes to coat magnetic particles is described in U.S. Pat. No. 5,508,880.
Kormann et al. (Kormann, Cl., Laun, H. M., and Richter, H. J., “MR Fluids with Nano-sized Magnetic Particles”, Proceedings of the 5th International Conference on Electrorheological Fluids, Magnetorheological Suspensions and Associated Technology, World Scientific, Publisher, pp. 362-367, Jul. 10-14, 1995) have synthesized and characterized MR fluids containing nanosized magnetic particles. Because of the presence of the nanoparticles, these fluids exhibited very low shear stress.
Several hydrogen bonded supramolecular polymer systems have been reported. Hydrogen bonding of polystyrene-b-poly(4vinylpyridine) has been reported with nonadecylphenol (NDP) (J. Ruokolainen et al., Advanced Materials (1999), 11, 777-78) and pentadecylphenol (PDP) (J. Ruokolainen et al., Science (1998), 280, 557-560). Ikkala and coworkers (J. Ruokolainen et al., Advanced Materials (1999), 11, 777-78) reported supramolecular polymers forming hierarchical morphologies like lamellar-within lamellar, lamellar-within-cylindrical, cylindrical-within-lamellar, spherical-within-lamellar, and lamellar-within-spherical. A comb copolymer supramolecular system was reported to be formed by either Poly4VP(NDP)1.0 or Poly4VP(PDP)1.0 complex (J. Ruokolainen et al., Science (1998), 280, 557-560). Hydrogen bonding of polyaniline with 4-hexylresorcinol (Hres) has been reported (H. Kosonen, et al., Macromolecules (2000), 33, 8671-8675). Hydrogen-bonding of poly(2,5-pyridinediyl) with alkylphenols has been reported (Ikkala O., et al. Advanced. Materials (1999) 11, 1206-1210). Hydrogen bonding of diacid bipyridal ethylene has been reported (Jianwei Xu, Macromolecules (2002),35, 8846-8851). Pourcain and his coworker used the hydrogen bond between carboxylic acid and pyridines to self assemble an extended chain (C. B. St. Pourcain; A. C. Griffin; (1995), Macromolecules, 28, 4116-4121).
Several supramolecular systems involving electrostatic interactions have been reported. Supramolecular systems based on electrostatic interactions between poly(styrenesulfonate) and n-alkyltrimethylammonium surfactants have been reported (Charl F. J. Faul and Markus Antonietti Advanced Materials (2003), 15, 673-683). Cohesive coatings with low surface tensions were reportedly formed through electrostatic interactions of polyelectrolyte and diverse fluorinated surfactant complex (Faul and Antionietti, 2003 supra). Supramolecular interactions between poly(diallyldimethylammonium chloride) (PDADMACI) and sodium dodecyl sulfate have also been reported (Fengji Yeh, et al., J. Am. Chem. Soc., (1996), 118, 6615-6618).
Several supramolecular systems involving hydrophobic/hydrophilic interaction have been reported. Nanophase-segregated graft copolymers of poly(vinyl acetate) (PVAc) backbones branched with poly(dimethylsiloxane) (PDMS) or poly(styrene) (PS) have been reported (Heather D. Maynard et al., Polymer 42 (2001) 7567-7574). Supramolecular behavior of block copolymers (AB diblock or AGA, ABC triblock) has been reported (Frank S. Bates, Glenn H. Fredickson, Annu. Rev. Phys. Chem. (1990) 41 525-55). In the phase diagram of poly(oxyethylene)alkyl ether and poly(oxyethylene)-poly(dimethylsiloxane) diblock copolymers, two lamellar phases were reported to coexist, one containing surfactant rich thin bilayers and the other copolymer-rich thick bilayers (Aramaki, Md. et al. Macromolecules 36 (2003) 9443-9450). Block copolymers dissolved in block-selective solvents also self-assemble into a variety of morphologies including spheres, cylinders, and vesicles.
Several supramolecular systems involving metal coordination bonding have been reported. Terpyridine-terminated polystyrene-block-poly(ethylene oxide) coordinated with transition metal chlorides (i.e. ruthenium ions) have been reported (M. Al-Hussein et al. Macromolecules (2003), 36, 9281-9284). Poly(4-vinylpyridine) coordinated with 2,6-bis(octylaminomethyl)-pyridine and Zn(dodecylbenzenesulfonate) Zn(DBS)2 has been reported (Sami Valkama, et al. Macromolecular Rapid Communications (2003) 24 556-560) Systems based on 2,2′:6′,2″-terpyridine based polymer have also been reported (Ulich S. Schubert, Macrolol. Symp. (2001), 163 177-187; Ulrich S. Schubert, Macromol. Rapid Commun. (2000), 21, 1156-1161).
Systems based on liquid crystal interactions and π-π stacking have also been reported. A poly(9,9 bis(ethylhexyl)-fluorene-2,7-diyl) system has been reported (Matti Knaapila et al., J. Phys. Chem. B (2004), 108, 10711-10720). Polyimide systems have also been reported (Hans R. Kricheldorf and Volker Linzer, (1995), Polymer Vol. 9, 1893-1902; T. I Kaneko et al.,”, Macromolecules (1997), 30, 4224-4246; H. W. Huanga, et al. (1999), Polymer 40, 3821{umlaut over ( )}C3828; S.-J. Sung, et al., Synthetic Metals 117 (2001) 277-279).
A polymer containing 3,4-dichloro-2,5-diamido-substituted pyrrole anion dimer forming a supramolecular system via anion-anion assembly has also been reported (Philip A. Gale “Anion-anion assembly: A new class of anionic supramolecular polymer containing 3,4-dichloro-2,5-diamido-substituted pyrrole anion dime” J. Am. Chem. Soc. (2002), 124, 11228-11229).
Supramolecular polymer gel systems have been reported. Chujo et al. report syntheses of metal induced gelation of polyoxazolines containing bipyridyl units. .(Chujo, Y.; Sada, K.; Safgusa, T. Macromolecules (1993), 26, 6320-6323; Chujo, Y.; Sada, K.; Safgusa, T. Macromolecules (1993), 26, 6315-631). Yeh et al. report nanoscale supramolecular structures in the gels of poly(diallyldimethylammonium chloride) interacting with sodium dodecyl sulfate (F. Yeh, et al. J. Am. Chem. Soc. (1996) 118 6615-6618).
Shear yield stress and off-state viscosity are important design parameters for MR materials utilized in MR devices that are used for vibration control such as in dampers, shock absorbers, clutches and engine mounts. A material with high shear yield stress permits the development of high torque output devices. High yield stress also permits the development of micromechanical devices. The present invention describes a class of MR materials with high shear yield stress, controllable off-state viscosity and fluid stability. The viscoelastic properties of this material can be designed through control of their storage and loss moduli.